Hillary Clinton supports gay marriage. This is a major shift. Yet, as someone who wrote a book on Clinton’s faith, I can’t say I’m surprised.

Hillary Clinton is a lifelong Christian, a committed member of the United Methodist Church. She had long been committed to marriage as between one man and one woman. As once noted by the Rev. Don Jones, Clinton’s youth minister and mentor in Park Ridge, Ill., in the 1960s: “Surely, she is for gay rights. There’s no question about that. But I think both she and Bill still think of heterosexuality as normative.”

It was in that spirit that Hillary Clinton supported the 1996 Defense of Marriage Act, signed into law by her husband, President Bill Clinton. The law bans federal recognition of gay marriage and allows states to ignore same-sex unions licensed elsewhere.

Not long after that, her position on various gay rights issues was consistently challenged and began a slow evolution—most notably as she campaigned for New York’s Senate seat in 2000. In December 1999, speaking to gay contributors at a New York fundraiser, she said she supported “domestic-partnership measures” that permitted homosexual partners to receive the same benefits as married couples. Significantly, however, her spokesperson stressed that she continued to support the Defense of Marriage Act. She made that stance clear a few weeks later in White Plains, N.Y.: “Marriage has historic, religious and moral content that goes back to the beginning of time, and I think a marriage is as a marriage has always been, between a man and a woman.”

Nonetheless, Hillary Clinton’s position remained a burning, unavoidable issue.

In June 2003, Sen. Clinton introduced legislation to grant homosexual couples the same rights as heterosexual couples. With that, her position on marriage had not substantially or publicly changed. Privately, however, she might have been starting to reconsider.

In the New York Post the next month, Deborah Orin reported that Mrs. Clinton suddenly wouldn’t take a position on the Defense of Marriage Act, and that Bill Clinton’s office was notably silent on whether the former president still backed the bill he signed into law. Orin quoted Hillary Clinton spokeswoman Karen Dunn, who said, “This issue is in a state of evolution.”

It sure was.

What was going on? Was Mrs. Clinton suddenly conflicted?

On June 18, 2003, she gave an interview to New York’s WNYC, where she affirmed: “You know, marriage has a meaning that … I think should be kept as it historically has been, but I see no reason whatsoever why people in committed relationships can’t have … many of the same rights and the same … respect for their unions that they are seeking. And I would like to see that be more accepted than it is. … I also think that we can realize the same results for many committed couples by urging that states and localities adopt civil union and domestic partnership laws.”

Her position remained fairly clear, but she was expressing it with rising ambivalence. I wrote in my 2007 book that it seemed that if the public changed its attitude on gay marriage, she would probably follow suit.

As late as the 2008 presidential race, Clinton still opposed same-sex marriage, advocating civil unions and leaving the legality of marriage to the states.

All of this changed this week, when the Human Rights Campaign, a gay-rights group with which Clinton has personal ties, posted a video where Clinton came out for gay marriage. The timing comes as the Supreme Court readies to hear two pivotal cases on gay marriage. “LGBT Americans are our colleagues, our teachers, our soldiers, our friends, our loved ones, and they are full and equal citizens and deserve the rights of citizenship,” said Clinton. “That includes gay marriage.”

Alas, here we are: Hillary Clinton favors gay marriage.

Some will charge that Clinton has embraced gay marriage out of political opportunism, that she sees the direction of her party, and therefore looking ahead to the 2016 presidential race, there’s no way she would oppose gay marriage.

Perhaps there’s some truth to the claims, but I interpret her position as steadily evolving. It’s an honest shift, one that thrills liberals.